Fatty livers are rarely used for partial liver transplantation due to the fear of primary non-function. These studies are to elucidate mechanisms and to develop strategies to prevent failure of fatty partial grafts. We will use reduced-size rat liver transplantation to test the unique hypotheses that steatosis and partial liver transplantation synergistically increase reactive oxygen and nitrogen species (ROS and RNS), inhibit mitochondrial function and suppress liver regeneration. In Aim 1, we will investigate if steatosis increases graft failure after partial liver transplantation. Fatty livers will be induced by high fat diet and choline-deficient diet, respectively, and reduced to 30% to 50% of original size. We will assess survival, liver function, and histology after transplantation as a function of steatosis, graft volume and cold storage time. In Aim 2, we will test the hypothesis that ROS and RNS are increased in high-fat diet-induced fatty partial grafts, leading to injury. ROS will be determined by the spin-trapping technique and immunohistochemistry for 4-hydroxynonenal and RNS will be assessed as nitrotyrosine and nitrite/nitrate levels. We expect that ROS and RNS production will be higher in fatty than lean partial grafts. We will also identify cellular sources of ROS and RNS using fluorescent intravital multiphoton microscopy. The effects of antioxidants (Ad-superoxide dismutase, N-acetylcysteine and polyphenols) and antinitrative therapies (nitric oxide synthase inhibitors) on survival and injury of fatty partial grafts will be evaluated. In Aim 3, effects of steatosis and graft volume on energy supply will be evaluated. Uncoupling protein 2, mitochondrial permeability transition and respiratory chain activity will be determined to elucidate the mechanisms of defective energy production, and effects of mitochondrial permeability transition inhibitors and antioxidant and antinitrative therapies on mitochondrial function will be evaluated. In Aim 4, the effects of steatosis and graft volume on liver regeneration will be assessed. Cell proliferation and factors regulating regeneration (cytokines, transcription factors, growth factors, and cell cycle related genes) will be evaluated. In addition, we will investigate if protection of mitochondria function and antioxidative and antinitrative therapies improve liver regeneration. Taken together, we expect that this work will provide fundamental new insights into the mechanisms underlying reduced-size fatty graft failure and develop mechanism-based strategies to increase the use and improve the outcome of fatty livers for partial liver transplantation in the clinic.